1. Field of the Invention
The present invention relates to a method for producing a mold for use in molding a two-dimensional or three-dimensional long member having a straightness, a curvature, or a twist such as a stringer for aircraft by using a prepreg made of a composite material.
2. Description of the Related Art
Molds for producing a long structural member for aircraft made of a composite material such as carbon fiber are generally produced from metal or a composite material.
When the mold is produced from metal, a master model is produced, and a casting mold is produced using the master model. Molten metal is poured into the casting mold to produce a casting. The casting is then mechanically processed into a require shape or size, or to obtain a required surface roughness. Since the mold needs to be produced through the above complicated processes, the cost for the same increases and a long lead time becomes necessary.
There is also a method of directly performing mechanical processing on a metal block including a required size. However, the material is largely wasted, and it also takes a longer time to process the material. When the mold is made of metal, there is also a problem that the mold is heavier than the mold made of a composite material.
When the mold is produced from a composite material, a following procedure needs to be performed.
An inverted mold corresponding to the mold is produced by mechanical processing. Prepregs for the mold are laminated on the inverted mold, subjected to bagging, and pressurized and heated in an autoclave or the like to be cured.
While the inverted mold is produced from an inorganic porous material such as plaster, or epoxy resin, the materials have low strength and are brittle materials. Thus, a long inverted mold is difficult to handle. The material size is also limited, so that there is an inconvenience that the materials having a cut length need to be bonded together so as to produce a long product.
In autoclave molding, the materials are exposed to a curing temperature of the prepreg. The inorganic porous material such as plaster or the epoxy resin is thereby reduced in strength, and a crack may occur in the inverted mold due to a molding pressure or a thermal stress generated by a difference in linear expansion coefficient.
There is also a production method of performing mechanical processing on a material block in a similar manner to the mold made of metal. However, since a material large enough to include a three-dimensional shape is required, there are problems that the material is wasted, it takes a longer processing time, and when a long member is processed, a long material has low marketability.
A two-dimensional straight mold is produced by a normal continuous pultrusion molding method disclosed in Japanese Patent Laid-Open Publication No. 01-004315 (Patent Document 1).
A mold having a curve or a twist is disclosed in Japanese Patent Laid-Open Publication No. 2005-186558 (Patent Document 2) or No. 2009-234046 (Patent Document 3).
In the related art described above, the inverted mold needs to be produced before the mold is produced in both the cases of the metal mold and the composite material mold, or the material including the size and shape of a molded article is required.
The inverted mold (the casting mold) for the metal mold needs to be produced through the complicated processes. The inverted mold for the composite material mold is less reliable with respect to the strength and the resistance to heat. In both the cases, a period and a cost for producing the mold are increased.
It is an object of the present invention to provide a method for producing a mold made of a composite material for a long member at a low cost in a short period of time without producing an inverted mold and without any need for a material including the size and shape of a molded article.